Vickers indentation behavior of several commercial glasses at high temperatures

The Vickers indentation behavior of five commercial glasses has been investigated as a function of temperature. The glasses included: (i) soda-lime-silica Float glass, (ii) lead-alkali silicate, (iii) 7740 PyrexTM borosilicate, (iv) potassium phosphate, and (v) lanthanum borate. A recording microindentation system was constructed to allow Vickers indentation testing to be conducted at temperatures significantly above room temperature. The Vickers hardness was observed to decrease continuously with increasing temperature for all glasses, with the exception of the 7740 PyrexTM glass. Decreases in hardness were attributed to decreases in elastic moduli and bond strength with increasing temperature. The lengths of median-radial cracks around indentations in several glasses were observed to first increase, and then decrease, with increasing temperature. The first of this behavior was attributed to initial increases of the crack driving force, characterized by the quantity (E/H), as well as to a decrease in fracture surface energy. Viscous flow at higher temperatures was believed responsible for a reduction in the crack driving force and crack tip stress, resulting in an eventual decrease in crack length. Viscoelastic behavior of the Float glass was characterized by a rate-dependent hardness and indentation crack pattern. Load–displacement traces indicated an increase in the work of indentation and residual indentation depthwith increasing temperature for all glasses.